1. Field of the Invention
The present invention relates to an improvement in the cut sheet feeder for feeding cut sheets separately one by one comprising sheet feeding and conveying means for contacting with the obverse side of a first sheet to move the first sheet forwardly by frictional force, and arresting means for contacting with the reverse side of a next sheet to arrest forward movement of the next sheet, the frictional force applied by the sheet feeding and conveying means being larger than the frictional force applied by the arresting means.
2. Prior Art
In various office automation systems, cut sheets each having predetermined dimensions are stacked to be fed separately one by one securely at high speed. The known cut sheet feeders include the friction type device in which cut sheets are fed by utilizing frictional force, and the suction type device in which cut sheets are fed by utilizing suction force developed by pneumatic negative pressure.
In the friction type device, an obverse side of a first cut sheet to be fed into the system is pressed by conveying means, such as a roller or a conveyor belt, so that the sheet is pulled by the frictional force generated between the sheet and the conveying means. However, in this type cut sheet feeder, due to the friction between the reverse side of the first sheet and the obverse side of the next sheet, there arises a tendency that the next sheet is moved together with the first sheet to induce a problem of overlapped feeding.
In order to prevent such an overlapped feeding, it has been proposed to provide a friction pad for contacting with the reverse side of the sheet to arrest forward movement of the next sheet, or to provide a friction roller contacting with the reverse side of the sheet and rotating in the direction for moving the next sheet backwards. However, in the device in which frictional force is utilized for the separation of adjacent sheets, since the difference in frictional force between the friction at the interface of the friction pad or roller and the reverse side of the sheet and the friction at the interface of adjacent sheets is utilized, the operation of separating the sheets becomes unstable as the quality or thickness of the sheet material is changed or the coefficient of friction is changed during the operation.
On the other hand, since the sheet is sucked and conveyed in the device in which suction force is utilized, a large size pneumatic pump must be assembled for developing high negative or sucking pressure. In addition, the sucking pressure must be controlled depending on the quality and thickness of the sheet material to be sucked, and the position of the sucking port must be shifted when the size of the sheet is changed.